1. Field of the Invention
The present invention relates to a gas-cylinder valve to be employed in a gas cylinder which serves to store a dangerous gas which must not be leaked outside, for example a poison gas, an inflammable gas and the like.
2. Background of the Prior Art
For safe transfer of a gas contained within a gas cylinder, the basic construction of the gas-cylinder valve is disclosed, for example in U.S. Pat. No. 4,768,543 (date of Patent: Sept. 6, 1988).
In this known structure a gas inlet is in communication with a gas outlet through a gas inlet passage, a gas supply valve chamber and a gas outlet passage within a valve box of the gas-cylinder valve, said gas supply valve chamber is provided with a gas supply valve body and said gas supply valve body is adapted to be operatively opened and closed with respect to a valve seat of the gas supply valve chamber by means of a gas supply valve operation means.
In this basic construction, conventionally the gas supply valve chamber is constructed so as to be always in communication with the gas outlet through the gas outlet passage.
However, in this gas-cylinder valve, the gas outlet thereof is opened to the atmosphere when such occur as mentioned in the following:
(a) At the time of the removal of a gas charging connector from the gas outlet after the completion of the gas charging into the gas cylinder by a gas manufacturer.
(b) In the case that the outlet of the gas-cylinder valve is not closed by means of an outlet cap during the custody as well as the transportation of the gas cylinder.
(c) During the connection of a gas takeout connector to the gas outlet of the gas-cylinder valve after the removal of the outlet cap by a user.
In case that the gas outlet of the gas-cylinder valve is opened to the atmosphere in that way, there are the following problems associated with the gas-cylinder valve having the above-mentioned conventional construction.
Since the gas supply valve chamber is always in communication with the gas outlet through the gas outlet passage, the atmospheric air is apt to enter the gas supply valve chamber through the gas outlet and the gas outlet passage together with foreign substances such as moisture, rain, dust and the like. Since these foreign substances are apt to corrode and damage the gas supply valve body and the valve seat, it is apprehended that a dangerous gas stored within a gas cylinder may in time leak to the atmosphere.
For example, if the gas stored within the gas cylinder is Cl.sub.2 (Chloride), HCl (Hydrogen Chloride), WF.sub.6 (Hexafluotungsten), Si.sub.2 F.sub.6 (Hexafluodisilan) or BF.sub.3 (Boron Trifluoride), when moisture and/or rain enter the gas supply valve chamber, such a gas causes a chemical reaction with the moisture and the rain within the gas supply valve chamber so as to make strong acid liquid at the beginning of the takeout of the gas within the gas cylinder after opening the gas supply valve body. The gas supply valve body and the valve seat are accidentally corroded by the strong acid liquid.
Also when dust enters the gas supply valve chamber, it may locate between the gas supply valve body and the valve seat at the time of the opening and closing operation of the gas supply body so that these members are eventually damaged.